[PATCH v11 3/3] dmaengine: switchtec-dma: Implement descriptor submission

Logan Gunthorpe
2025-12-15T18:40:58Z

From: Kelvin Cao <kelvin.cao@microchip.com>

On prep, a spin lock is taken and the next entry in the circular buffer
is filled. On submit, the spin lock just needs to be released as the
requests are already pending.

When switchtec_dma_issue_pending() is called, the sq_tail register
is written to indicate there are new jobs for the dma engine to start
on.

Pause and resume operations are implemented by writing to a control
register.

Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Co-developed-by: George Ge <george.ge@microchip.com>
Signed-off-by: George Ge <george.ge@microchip.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
drivers/dma/switchtec_dma.c | 221 ++++++++++++++++++++++++++++++++++++
1 file changed, 221 insertions(+)

diff --git a/drivers/dma/switchtec_dma.c b/drivers/dma/switchtec_dma.c
index 648eabc0f5da..9f95f8887dd2 100644
--- a/drivers/dma/switchtec_dma.c
+++ b/drivers/dma/switchtec_dma.c
@@ -33,6 +33,8 @@ MODULE_AUTHOR("Kelvin Cao");
#define SWITCHTEC_REG_SE_BUF_CNT 0x98
#define SWITCHTEC_REG_SE_BUF_BASE 0x9a

+#define SWITCHTEC_DESC_MAX_SIZE 0x100000
+
#define SWITCHTEC_CHAN_CTRL_PAUSE BIT(0)
#define SWITCHTEC_CHAN_CTRL_HALT BIT(1)
#define SWITCHTEC_CHAN_CTRL_RESET BIT(2)
@@ -194,6 +196,11 @@ struct switchtec_dma_hw_se_desc {
__le16 sfid;
};

+#define SWITCHTEC_SE_DFM BIT(5)
+#define SWITCHTEC_SE_LIOF BIT(6)
+#define SWITCHTEC_SE_BRR BIT(7)
+#define SWITCHTEC_SE_CID_MASK GENMASK(15, 0)
+
#define SWITCHTEC_CE_SC_LEN_ERR BIT(0)
#define SWITCHTEC_CE_SC_UR BIT(1)
#define SWITCHTEC_CE_SC_CA BIT(2)
@@ -231,6 +238,8 @@ struct switchtec_dma_desc {
bool completed;
};

+#define SWITCHTEC_INVALID_HFID 0xffff
+
#define SWITCHTEC_DMA_SQ_SIZE SZ_32K
#define SWITCHTEC_DMA_CQ_SIZE SZ_32K

@@ -603,6 +612,210 @@ static void switchtec_dma_synchronize(struct dma_chan *chan)
spin_unlock_bh(&swdma_chan->complete_lock);
}

+static struct dma_async_tx_descriptor *
+switchtec_dma_prep_desc(struct dma_chan *c, u16 dst_fid, dma_addr_t dma_dst,
+ u16 src_fid, dma_addr_t dma_src, u64 data,
+ size_t len, unsigned long flags)
+ __acquires(swdma_chan->submit_lock)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(c, struct switchtec_dma_chan, dma_chan);
+ struct switchtec_dma_desc *desc;
+ int head, tail;
+
+ spin_lock_bh(&swdma_chan->submit_lock);
+
+ if (!swdma_chan->ring_active)
+ goto err_unlock;
+
+ tail = READ_ONCE(swdma_chan->tail);
+ head = swdma_chan->head;
+
+ if (!CIRC_SPACE(head, tail, SWITCHTEC_DMA_RING_SIZE))
+ goto err_unlock;
+
+ desc = swdma_chan->desc_ring[head];
+
+ if (src_fid != SWITCHTEC_INVALID_HFID &&
+ dst_fid != SWITCHTEC_INVALID_HFID)
+ desc->hw->ctrl |= SWITCHTEC_SE_DFM;
+
+ if (flags & DMA_PREP_INTERRUPT)
+ desc->hw->ctrl |= SWITCHTEC_SE_LIOF;
+
+ if (flags & DMA_PREP_FENCE)
+ desc->hw->ctrl |= SWITCHTEC_SE_BRR;
+
+ desc->txd.flags = flags;
+
+ desc->completed = false;
+ desc->hw->opc = SWITCHTEC_DMA_OPC_MEMCPY;
+ desc->hw->addr_lo = cpu_to_le32(lower_32_bits(dma_src));
+ desc->hw->addr_hi = cpu_to_le32(upper_32_bits(dma_src));
+ desc->hw->daddr_lo = cpu_to_le32(lower_32_bits(dma_dst));
+ desc->hw->daddr_hi = cpu_to_le32(upper_32_bits(dma_dst));
+ desc->hw->byte_cnt = cpu_to_le32(len);
+ desc->hw->tlp_setting = 0;
+ desc->hw->dfid = cpu_to_le16(dst_fid);
+ desc->hw->sfid = cpu_to_le16(src_fid);
+ swdma_chan->cid &= SWITCHTEC_SE_CID_MASK;
+ desc->hw->cid = cpu_to_le16(swdma_chan->cid++);
+ desc->orig_size = len;
+
+ head++;
+ head &= SWITCHTEC_DMA_RING_SIZE - 1;
+
+ /*
+ * Ensure the desc updates are visible before updating the head index
+ */
+ smp_store_release(&swdma_chan->head, head);
+
+ /* return with the lock held, it will be released in tx_submit */
+
+ return &desc->txd;
+
+err_unlock:
+ /*
+ * Keep sparse happy by restoring an even lock count on
+ * this lock.
+ */
+ __acquire(swdma_chan->submit_lock);
+
+ spin_unlock_bh(&swdma_chan->submit_lock);
+ return NULL;
+}
+
+static struct dma_async_tx_descriptor *
+switchtec_dma_prep_memcpy(struct dma_chan *c, dma_addr_t dma_dst,
+ dma_addr_t dma_src, size_t len, unsigned long flags)
+ __acquires(swdma_chan->submit_lock)
+{
+ if (len > SWITCHTEC_DESC_MAX_SIZE) {
+ /*
+ * Keep sparse happy by restoring an even lock count on
+ * this lock.
+ */
+ __acquire(swdma_chan->submit_lock);
+ return NULL;
+ }
+
+ return switchtec_dma_prep_desc(c, SWITCHTEC_INVALID_HFID, dma_dst,
+ SWITCHTEC_INVALID_HFID, dma_src, 0, len,
+ flags);
+}
+
+static dma_cookie_t
+switchtec_dma_tx_submit(struct dma_async_tx_descriptor *desc)
+ __releases(swdma_chan->submit_lock)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(desc->chan, struct switchtec_dma_chan, dma_chan);
+ dma_cookie_t cookie;
+
+ cookie = dma_cookie_assign(desc);
+
+ spin_unlock_bh(&swdma_chan->submit_lock);
+
+ return cookie;
+}
+
+static enum dma_status switchtec_dma_tx_status(struct dma_chan *chan,
+ dma_cookie_t cookie, struct dma_tx_state *txstate)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(chan, struct switchtec_dma_chan, dma_chan);
+ enum dma_status ret;
+
+ ret = dma_cookie_status(chan, cookie, txstate);
+ if (ret == DMA_COMPLETE)
+ return ret;
+
+ switchtec_dma_cleanup_completed(swdma_chan);
+
+ return dma_cookie_status(chan, cookie, txstate);
+}
+
+static void switchtec_dma_issue_pending(struct dma_chan *chan)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(chan, struct switchtec_dma_chan, dma_chan);
+ struct switchtec_dma_dev *swdma_dev = swdma_chan->swdma_dev;
+
+ /*
+ * Ensure the desc updates are visible before starting the
+ * DMA engine.
+ */
+ wmb();
+
+ /*
+ * The sq_tail register is actually for the head of the
+ * submisssion queue. Chip has the opposite define of head/tail
+ * to the Linux kernel.
+ */
+
+ rcu_read_lock();
+ if (!rcu_dereference(swdma_dev->pdev)) {
+ rcu_read_unlock();
+ return;
+ }
+
+ spin_lock_bh(&swdma_chan->submit_lock);
+ writew(swdma_chan->head, &swdma_chan->mmio_chan_hw->sq_tail);
+ spin_unlock_bh(&swdma_chan->submit_lock);
+
+ rcu_read_unlock();
+}
+
+static int switchtec_dma_pause(struct dma_chan *chan)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(chan, struct switchtec_dma_chan, dma_chan);
+ struct chan_hw_regs __iomem *chan_hw = swdma_chan->mmio_chan_hw;
+ struct pci_dev *pdev;
+ int ret;
+
+ rcu_read_lock();
+ pdev = rcu_dereference(swdma_chan->swdma_dev->pdev);
+ if (!pdev) {
+ ret = -ENODEV;
+ goto unlock_and_exit;
+ }
+
+ spin_lock(&swdma_chan->hw_ctrl_lock);
+ writeb(SWITCHTEC_CHAN_CTRL_PAUSE, &chan_hw->ctrl);
+ ret = wait_for_chan_status(chan_hw, SWITCHTEC_CHAN_STS_PAUSED, true);
+ spin_unlock(&swdma_chan->hw_ctrl_lock);
+
+unlock_and_exit:
+ rcu_read_unlock();
+ return ret;
+}
+
+static int switchtec_dma_resume(struct dma_chan *chan)
+{
+ struct switchtec_dma_chan *swdma_chan =
+ container_of(chan, struct switchtec_dma_chan, dma_chan);
+ struct chan_hw_regs __iomem *chan_hw = swdma_chan->mmio_chan_hw;
+ struct pci_dev *pdev;
+ int ret;
+
+ rcu_read_lock();
+ pdev = rcu_dereference(swdma_chan->swdma_dev->pdev);
+ if (!pdev) {
+ ret = -ENODEV;
+ goto unlock_and_exit;
+ }
+
+ spin_lock(&swdma_chan->hw_ctrl_lock);
+ writeb(0, &chan_hw->ctrl);
+ ret = wait_for_chan_status(chan_hw, SWITCHTEC_CHAN_STS_PAUSED, false);
+ spin_unlock(&swdma_chan->hw_ctrl_lock);
+
+unlock_and_exit:
+ rcu_read_unlock();
+ return ret;
+}
+
static void switchtec_dma_desc_task(unsigned long data)
{
struct switchtec_dma_chan *swdma_chan = (void *)data;
@@ -733,6 +946,7 @@ static int switchtec_dma_alloc_desc(struct switchtec_dma_chan *swdma_chan)
}

dma_async_tx_descriptor_init(&desc->txd, &swdma_chan->dma_chan);
+ desc->txd.tx_submit = switchtec_dma_tx_submit;
desc->hw = &swdma_chan->hw_sq[i];
desc->completed = true;

@@ -1064,10 +1278,17 @@ static int switchtec_dma_create(struct pci_dev *pdev)

dma = &swdma_dev->dma_dev;
dma->copy_align = DMAENGINE_ALIGN_8_BYTES;
+ dma_cap_set(DMA_MEMCPY, dma->cap_mask);
+ dma_cap_set(DMA_PRIVATE, dma->cap_mask);
dma->dev = get_device(&pdev->dev);

dma->device_alloc_chan_resources = switchtec_dma_alloc_chan_resources;
dma->device_free_chan_resources = switchtec_dma_free_chan_resources;
+ dma->device_prep_dma_memcpy = switchtec_dma_prep_memcpy;
+ dma->device_tx_status = switchtec_dma_tx_status;
+ dma->device_issue_pending = switchtec_dma_issue_pending;
+ dma->device_pause = switchtec_dma_pause;
+ dma->device_resume = switchtec_dma_resume;
dma->device_terminate_all = switchtec_dma_terminate_all;
dma->device_synchronize = switchtec_dma_synchronize;
dma->device_release = switchtec_dma_release;
--
2.47.3